x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

It appears that the BayTrail-T class of hardware requires EFI in order
to powerdown and reboot and no other reliable method exists.

This quirk is generally applicable to all hardware that has the ACPI
Hardware Reduced bit set, since usually ACPI would be the preferred
method.

Cc: Len Brown <len.brown@intel.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

3 files changed, 45 insertions, 2 deletions

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 9043f365ebf5..044a2fd3c5fe 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -183,6 +183,8 @@ extern struct efi_config *efi_early;
 #define efi_call_early(f, ...)						\
 	efi_early->call(efi_early->f, __VA_ARGS__);
 
+extern bool efi_reboot_required(void);
+
 #else
 /*
  * IF EFI is not configured, have the EFI calls return -ENOSYS.
@@ -195,6 +197,10 @@ extern struct efi_config *efi_early;
 #define efi_call5(_f, _a1, _a2, _a3, _a4, _a5)		(-ENOSYS)
 #define efi_call6(_f, _a1, _a2, _a3, _a4, _a5, _a6)	(-ENOSYS)
 static inline void parse_efi_setup(u64 phys_addr, u32 data_len) {}
+static inline bool efi_reboot_required(void)
+{
+	return false;
+}
 #endif /* CONFIG_EFI */
 
 #endif /* _ASM_X86_EFI_H */
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 09e709fd1830..17962e667a91 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -28,6 +28,7 @@
 #include <linux/mc146818rtc.h>
 #include <asm/realmode.h>
 #include <asm/x86_init.h>
+#include <asm/efi.h>
 
 /*
  * Power off function, if any
@@ -401,12 +402,25 @@ static struct dmi_system_id __initdata reboot_dmi_table[] = {
 
 static int __init reboot_init(void)
 {
+	int rv;
+
 	/*
 	 * Only do the DMI check if reboot_type hasn't been overridden
 	 * on the command line
 	 */
-	if (reboot_default)
-		dmi_check_system(reboot_dmi_table);
+	if (!reboot_default)
+		return 0;
+
+	/*
+	 * The DMI quirks table takes precedence. If no quirks entry
+	 * matches and the ACPI Hardware Reduced bit is set, force EFI
+	 * reboot.
+	 */
+	rv = dmi_check_system(reboot_dmi_table);
+
+	if (!rv && efi_reboot_required())
+		reboot_type = BOOT_EFI;
+
 	return 0;
 }
 core_initcall(reboot_init);
diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index b4cb9182f155..1c7380da65ff 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -7,6 +7,7 @@
 #include <linux/slab.h>
 #include <linux/memblock.h>
 #include <linux/bootmem.h>
+#include <linux/acpi.h>
 #include <asm/efi.h>
 #include <asm/uv/uv.h>
 
@@ -265,3 +266,25 @@ void __init efi_apply_memmap_quirks(void)
 	if (is_uv_system())
 		set_bit(EFI_OLD_MEMMAP, &efi.flags);
 }
+
+/*
+ * For most modern platforms the preferred method of powering off is via
+ * ACPI. However, there are some that are known to require the use of
+ * EFI runtime services and for which ACPI does not work at all.
+ *
+ * Using EFI is a last resort, to be used only if no other option
+ * exists.
+ */
+bool efi_reboot_required(void)
+{
+	if (!acpi_gbl_reduced_hardware)
+		return false;
+
+	efi_reboot_quirk_mode = EFI_RESET_WARM;
+	return true;
+}
+
+bool efi_poweroff_required(void)
+{
+	return !!acpi_gbl_reduced_hardware;
+}